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Lec. 2 Types of Microorganisms Cariogenic in Animal Models

الكلية كلية طب الاسنان     القسم التقويم والاطفال وطب الاسنان الوقائي     المرحلة 5
أستاذ المادة حسن فليح فرحان السلطاني       6/7/2011 12:33:25 PM

Lec. 2                                           Preventive dentistry                            Dr. Hassan Wateefi

Types of Microorganisms Cariogenic in Animal Models:
It is now known that a number of different organisms include caries in appropriate test animals and some are selective for different sits of the dentition. The type of dental caries initiated by various bacteria in the germ free rat was shown in this table:

Smooth surface lesion

 

    Fissure lesion

 

 

Root surface lesions

 

S. Mutans

 

S. Mutans

 

S. Sanguis

 

S. Mutans

 

 

S. Salivarius

 

S. Salivarius            S.Mitior                        S. Feacalis    A.Viscosus                   A. naesiunclii             L. acidophilus
 L. casei

 

S. Salivarius

 

 

A.Viscosus

 

A. naesiuncli

 

Rothiaspeis

 

 

 

 

 

 

 

 

 

 

 

 

Microorganisms associated with dental caries in man:
Lactobacilli: -
During the twenties, several investigators reported an apparent correlation between the number of lactobacilli in the mouth & dental caries. Lactobacilli count definitely it’s correlated to activity of caries in man. If you have cavities& open carious cavities you will find there is high lactobacillus count. If the patient is caries free there is minimum lactobacillus. The observed fact that lactobacilli occur in relatively small number in dental plague indicate that they may not be a major etiological agent in the initiation of enamel caries.
However when micro colonies of lactobacilli do occur in plaque they contribute to caries process. The really important lactobacilli in initiation of caries in man can not be stated any certainty at resent. All most certainly an important part in destruction of dentine in established caries. So lactobacilli cause prominent of caries not initiation, so it start its action after caries has been established.

Streptococcus Mutans: -
The species was first demonstrated in (l924) by Clark and has been extensively studied in  recent years,  the name S. mutans was given to streptococci isolated from human teeth, because these species characteristically changes from a rod coccus shape to a rod shape under certain growth condition such as low PH. It has the ability to fermentate a wide range of CHO substrate and  producing acid.
Particular characteristic of S. mutans is the production of extra cellular polysaccharides glucan type from sucrose. Palther demonstrate that there are at least 5 serological different types of s. mutans (a, b, c, d and e). More recent1y the number of proposed serotypes has been increased to 7.
Streptococcus are G+ve,  catalase  –ve cocci  , sometime, appearing as short rod which may form chain under certain conditions of growth, from these species which are known. to form caries in animals are S. mutans, S. sangius, & S. salivarius, recently S. Mielerii’s have also shown to be cariogenic in gonobictic rats. Of these S. mutans most extensively investigated & appear to be more effective than other species in producing caries in mono-infected animals 

THEORIES OF CARIES ETIOLOGY
Chemical theory:
  Parmly (1819) rebelled against the vital theory and proposed that an unidentified (chemical agent) was responsible for caries. He stated that caries began on the enamel surface in locations where food putrefied and acquired sufficient dissolving power to produce the disease chemically. Support to chemical theory came from Robertson (1835) and Regnart (1938), who actually carried out experiments with different dilution of inorganic acids such as sulfuric and nitric acid and found that they corroded enamel and dentine.
Parasitic or septic theory:
In (1843) Erdl described filamentous parasites in the surfaces membrane and plaque of the teeth.  Shortly after that, Ficinus observed filamentous microorganisms, which he called it, Denticolae, in material taken from caries cavities. He implied that these bacteria caused decomposition of the enamel and then the dentin. Neither Erdl nor Ficinus explained how these organisms destroyed tooth structure.
Chemo parasitic (acidogenic) theory:
The chemo-parasitic theory is a blend of the above tow theories because it supposed that dental decay is initiated by dissolution of enamel by acids which are produced by MO. during fermentation of CHO.
Miller (1851) writings and experiments helped to establish this concept on a firm basis. He took extracted humans teeth and but it in a tube with bread and human saliva and but them in the incubator and follow up, after 6 months examined the teeth microscopically and found dissolution of enamel. On the other hand, Pasteur had discovered that microorganisms transform sugars to lactic acid in the process of fermentation.
Leber and Roltenstein (1867) presented additional experimental evidence implicating acids which made enamel porous and bacteria as the causative agents. They described a specific microorganism (Leptothrix buccalis) in tubules of carious dentin and thought that it was responsible for enlarging the tubules and facilitating the rapid penetration of acids.

Proteolysis theory:
Mature enamel is more highly mineralized than any other vertebrate tissue. The human tooth contains only about 1.5% to 2% organic material, of which 0.3% to 0.4% is protein. According to the proteolytic theory, the organic component is more vulnerable and is attacked by hydrolytic enzymes of microorganism. This precedes the loss of the inorganic phase.
Gottlieb (1944) maintained that the initial action was due to proteolytic enzymes attacking the lamellae, rod sheaths, tufts and walls of dentinal tubules. He suggested that a Staphylococcus aureus was involved because of the yellow pigmentation that he considerd pathognomonic feature of dental caries.
Pineus (1949) contended that proteolytic organisms first attacked the proteins elements, such as dental cuticle, and then destroyed the prism sheathes. The loosened prisms would then fall out mechanically. 


Proteolysis- chelation theory :
A chelate results from combing an inorganic metal with at least tow electron-rich functional groups in a single organic molecule. The chelating agent is a molecule capable of seizing and holding a metal ion in a, claw-like grip (Greek: chele=claw) and forming a heterocyclic ring. The atoms hold the metal ion are called ligands and are usually oxygen, nitrogen, or Sulfur.
In biology there are many well known chelates, including hemoglobin (containing iron), chlorophyl (containing magnesium), vitamin B-12 (containing cobalt), and the enzymes cytochrome oxidase (containing both iron & copper).
Chelation has been proposed as an explanation for tooth decay where by the inorganic components of enamel can be removed at neutral or alkaline PH. The proteolysis-chelation theory considers dental caries to be a bacterial distraction of teeth where the initial attack is essentially in organic component of enamel. The breaks down products of this organic mater have chelating properties and there by dissolve the minerals in the enamel.  Thus, both the organic & inorganic constituents of enamel are simultaneously demolished.

Auto immunity theory :
Epidemiological  data were analyzed by Burch and Jackson (1966), they concluded that some of the findings could not be explained by the conventional theories of caries etiology, for example, if caries develops on the mesial surface of a maxillary central incisor, it is reasonable to have caries on the adjacent surface. As both surfaces were formed and calcified simultaneously, share a common plaque and are exposed to identical diet. Their results however, showed that more teeth resist the spread of caries from a neighboring carious tooth. This theory proposes that mutation can occur causing the release of a protein called mitotic control protein (MCP). The protein released in the circulation may lead to disorders of ameloblast cells. Therefore, changes in the resistance of the enamel to acid attack will occur.  



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